Search

At present, the Kuramoto model is the standard and widely accepted theoretical approach for analyzing the synchronization of spin-torque nano-oscillators (STNOs) coupled by an interaction. Nevertheless, the oscillatory decaying regime and the initial condition (IC)-dependence (hysteretic) that exist in the synchronization of many types of STNOs cannot be explained by this model. In order to more precisely elucidate the physical mechanisms behind the two phenomena, in this paper we develop a generalized pendulum-like model based on the two common features of non-linear auto-oscillators: one is the stability of the amplitude/energy of dynamic states and the other is the non-linear dynamic state energy of oscillators. In this new model, we find that the Newtonian-like particle with sufficient kinetic energy can overcome the barrier of phase-locking potential to evolve into a stable asynchronization state, leading to the IC-dependent synchronization. Furthermore, due to the presence of kinetic energy, this particle can also oscillate around the minima of the phase-locking potential, leading to the oscillatory decaying regime. Thereby, in this work, we adopt this new model to analyze the IC-dependent mutual synchronization of perpendicular-to-plane-STNO pairs, and then we suggest that the initial conditions can be controlled to avoid such a phenomenon by using magnetic dipolar coupling.

Giant magnetoimpedance (GMI) was investigated from room temperature up to 823 K in an Fe-based nanocrystalline Fe73.0Cu1.0Nb2.5V1.0Si13.5B9.0 ribbon. With an increment of the measuring temperature (T), GMI shows notable enhancement followed by a declining dependence, yielding a maximum value around 603 K where the relative GMI is nearly four times that at room temperature. The field at the peak of the GMI vs Hdc curve decreases monotonically with T, but around T=603 K there superimposes a trough-shaped variation. The thermal evolution of the soft magnetic property and magnetic anisotropy is suggested to be responsible for the high-temperature GMI features. Discussion on the intergrain exchange magnetic coupling through the amorphous boundaries in the two-phase Fe-based nanocrystalline alloy is also given.

A high-frequency longitudinally driven giant magnetoimpedance (GMI) effect has been measured in stress-annealed Fe73Cu1Nb1.5V2Si13.5B9 nanocrystalline ribbons. Based on how the impedance phase varies with the external magnetic field, it becomes clear that the imaginary part of the complex permeability, μ″, which is related to magnetic losses, plays an important role in the high-frequency longitudinally driven GMI effect. The transverse anisotropy field Hk can be readily determined by a sharp minimum in the curve of the impedance phase as a function of the external magnetic field. This provides a new method for measuring the magnetic anisotropy field in such systems.

In this work, the low rank approximation concept is extended to the non-equilibrium Green's function (NEGF) method to achieve a very efficient approximated algorithm for coherent and incoherent electron transport. This new method is applied to inelastic transport in various semiconductor nanodevices. Detailed benchmarks with exact NEGF solutions show 1) a very good agreement between approximated and exact NEGF results, 2) a significant reduction of the required memory, and 3) a large reduction of the computational time (a factor of speed up as high as 150 times is observed). A non-recursive solution of the inelastic NEGF transport equations of a 1000 nm long resistor on standard hardware illustrates nicely the capability of this new method., Comment: 9 pages, 7 figures